diff --git a/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OkapiCoreTestStubs.kt b/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OkapiCoreTestStubs.kt
new file mode 100644
index 0000000..7c17b9d
--- /dev/null
+++ b/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OkapiCoreTestStubs.kt
@@ -0,0 +1,10 @@
+package com.softwaremill.okapi.core
+
+/**
+ * Shared no-op test doubles for okapi-core. A single source means a [TransactionRunner] contract
+ * change is a one-line edit, not a sweep across every scheduler/purger test.
+ */
+
+internal fun noOpTransactionRunner() = object : TransactionRunner {
+    override fun <T> runInTransaction(block: () -> T): T = block()
+}
diff --git a/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxPurgerTest.kt b/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxPurgerTest.kt
index f28b7b2..47de099 100644
--- a/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxPurgerTest.kt
+++ b/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxPurgerTest.kt
@@ -299,10 +299,6 @@ class OutboxPurgerTest : FunSpec({
     }
 })
 
-private fun noOpTransactionRunner() = object : TransactionRunner {
-    override fun <T> runInTransaction(block: () -> T): T = block()
-}
-
 private fun stubStore(onRemove: (Instant, Int) -> Int = { _, _ -> 0 }) = object : OutboxStore {
     override fun persist(entry: OutboxEntry) = entry
     override fun claimPending(limit: Int) = emptyList<OutboxEntry>()
diff --git a/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxSchedulerTest.kt b/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxSchedulerTest.kt
index cf29568..98af3ee 100644
--- a/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxSchedulerTest.kt
+++ b/okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxSchedulerTest.kt
@@ -133,10 +133,6 @@ class OutboxSchedulerTest : FunSpec({
     }
 })
 
-private fun noOpTransactionRunner() = object : TransactionRunner {
-    override fun <T> runInTransaction(block: () -> T): T = block()
-}
-
 private fun stubProcessor(onProcessNext: (Int) -> Unit): OutboxProcessor {
     val store = object : OutboxStore {
         override fun persist(entry: OutboxEntry) = entry
diff --git a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/DataSourceQualifierAutoConfigurationTest.kt b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/DataSourceQualifierAutoConfigurationTest.kt
index 08019f6..a7d0e7e 100644
--- a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/DataSourceQualifierAutoConfigurationTest.kt
+++ b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/DataSourceQualifierAutoConfigurationTest.kt
@@ -79,7 +79,3 @@ class DataSourceQualifierAutoConfigurationTest : FunSpec({
             }
     }
 })
-
-private fun noOpTransactionRunner() = object : TransactionRunner {
-    override fun <T> runInTransaction(block: () -> T): T = block()
-}
diff --git a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/LiquibaseAutoConfigurationTest.kt b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/LiquibaseAutoConfigurationTest.kt
index 8d97834..4cfe78f 100644
--- a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/LiquibaseAutoConfigurationTest.kt
+++ b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/LiquibaseAutoConfigurationTest.kt
@@ -511,7 +511,3 @@ private fun canLoadClass(fqcn: String, classLoader: ClassLoader): Boolean = try
 } catch (_: ClassNotFoundException) {
     false
 }
-
-private fun noOpTransactionRunner() = object : TransactionRunner {
-    override fun <T> runInTransaction(block: () -> T): T = block()
-}
diff --git a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OkapiSpringTestStubs.kt b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OkapiSpringTestStubs.kt
index da0d571..855f7e6 100644
--- a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OkapiSpringTestStubs.kt
+++ b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OkapiSpringTestStubs.kt
@@ -5,6 +5,7 @@ import com.softwaremill.okapi.core.MessageDeliverer
 import com.softwaremill.okapi.core.OutboxEntry
 import com.softwaremill.okapi.core.OutboxStatus
 import com.softwaremill.okapi.core.OutboxStore
+import com.softwaremill.okapi.core.TransactionRunner
 import org.springframework.beans.factory.support.BeanDefinitionBuilder
 import org.springframework.context.support.GenericApplicationContext
 import java.time.Instant
@@ -31,6 +32,10 @@ internal fun stubDelivererWithType(t: String) = object : MessageDeliverer {
     override fun deliver(entry: OutboxEntry) = DeliveryResult.Success
 }
 
+internal fun noOpTransactionRunner() = object : TransactionRunner {
+    override fun <T> runInTransaction(block: () -> T): T = block()
+}
+
 /**
  * Registers a bean via [GenericApplicationContext.registerBeanDefinition], optionally `@Primary`.
  * Collapses the `BeanDefinitionBuilder.genericBeanDefinition(...).beanDefinition.apply { isPrimary }`
diff --git a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OutboxProcessorAutoConfigurationTest.kt b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OutboxProcessorAutoConfigurationTest.kt
index a3ef1e4..56c7f86 100644
--- a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OutboxProcessorAutoConfigurationTest.kt
+++ b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OutboxProcessorAutoConfigurationTest.kt
@@ -227,7 +227,3 @@ private fun resolveSpringBootClass(vararg candidateFqcns: String): Class<*> {
         }
     } ?: error("None of $candidateFqcns resolves on this Spring Boot runtime; check spring-boot-starter-actuator on the test classpath.")
 }
-
-private fun noOpTransactionRunner() = object : TransactionRunner {
-    override fun <T> runInTransaction(block: () -> T): T = block()
-}
diff --git a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OutboxPurgerAutoConfigurationTest.kt b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OutboxPurgerAutoConfigurationTest.kt
index a25055a..9a7812a 100644
--- a/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OutboxPurgerAutoConfigurationTest.kt
+++ b/okapi-spring-boot/src/test/kotlin/com/softwaremill/okapi/springboot/OutboxPurgerAutoConfigurationTest.kt
@@ -101,7 +101,3 @@ class OutboxPurgerAutoConfigurationTest : FunSpec({
         scheduler.isRunning shouldBe false
     }
 })
-
-private fun noOpTransactionRunner() = object : TransactionRunner {
-    override fun <T> runInTransaction(block: () -> T): T = block()
-}